Tag Archive for Tag: AASHTO

Tag: AASHTO The AASHTO Classification System

The AASHTO system classifies soils into seven primary groups, named A-1 through A-7, based on their relative expected quality for road embankments, subgrades, subbases, and bases. Some of the groups are in turn divided into subgroups, such as A-1-a and A-1-b. Furthermore, a group index may be calculated to quantify a soil’s expected performance within a group. To determine a

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Tag: AASHTO AASHTO Classification System Examples

Example 15.1 Classify the soil shown by the solid curve in Fig. 15.1. Assume the soil is nonplastic. The following data are obtained: Percent passing No. 4 sieve: 90% Percent passing No. 10 sieve: 70% Percent passing No. 40 sieve: 23% Percent passing No. 200 sieve: 4% D60 size: 1.50 mm D30 size: 0.61 mm D10 size: 0.18 mm To classify

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Tag: AASHTO Member Design Example-LRFD

The design of a truss hanger by the AASHTO LRFD Specifications is presented subsequently. This is preceded by the following introduction to the LRFD member design provisions. LRFD Member Design Provisions Tension Members. The net area, An, of a member is the sum of the products of thickness and the smallest net width of each element. The width of each standard

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Tag: AASHTO Detailing for Buckling

Prevention of buckling is important in bridge design, because of the potential for collapse. Three forms of buckling must be considered in bridge design. Types of Buckling The first, and most serious, is primary buckling of an axially loaded compression member. Such column buckling may include Euler-type elastic buckling and inelastic buckling. This is a rare occurrence with highway bridges, attesting to

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Tag: AASHTO Repetitive Loadings

Most structural damage to steel bridges is the result of repetitive loading from trucks or wind. Often, the damage is caused by secondary effects, for example, when live loads are distributed transversely through cross frames and induce large out-of-plane distortions that were not taken into account in design of the structure. Such strains may initiate small fatigue cracks. Under repetitive loads, the cracks grow.

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Tag: AASHTO Fracture Control

Fracture-critical members are treated in the AASHTO LRFD Specifications and in the AASHTO ‘‘Guide Specifications for Fracture Critical Non-Redundant Steel Bridge Members.’’ A fracture-critical member (FCM) or member component is a tension member or component whose failure is expected to result in collapse of the bridge or the inability of the bridge to perform its function. Although the definition is limited to tension

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Tag: AASHTO Basic Allowable Stresses for Bridges

Table 11.16 lists the basic allowable stresses for highway bridges recommended in AASHTO  ‘‘Standard Specifications for Highway Bridges’’ for ASD. The stresses are related to the minimum yield strength Fy , ksi, or minimum tensile strength Fu, ksi, of the material in all cases except those for which stresses are independent of the grade of steel being used. The basic stresses may

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Tag: AASHTO Primary Design Considerations

The primary purpose of a highway bridge is to safely carry (geometrically and structurally) the necessary traffic volumes and loads. Normally, traffic volumes, present and future, determine the number and width of traffic lanes, establish the need for, and width of, shoulders, and the minimum design truck weight. These requirements are usually established by the owner s planning and highway design section using

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